U.S. Pat. No. 4,728,981 granted to Koek et al, Mar. 1, 1988 shows a linear printhead assembly including a linear array of light-emitting diodes (LED's) and a linear imaging lens array. A single row of LED's are imaged by the lens array onto a radiation sensitive surface. Such imaging lens arrays are commercially available as SELFOC (a trademark of Nippon Sheet Glass Co. Ltd.) lenses in a 1 or more row bundle of optical fibers as described in U.S. Pat. No. 3,658,407. Other linear lens arrays include reflecting surfaces, for example, roof mirror lens arrays are commercially available. For high resolution applications, linear lens arrays must be accurately positioned with respect to the array of LED's. Once positioned, the lens and LED assembly must in turn be positioned accurately with respect to the photosensitive surface.
The Koek patent describes a set of screws and slots for adjusting the distance between the LED array and the lens array as a first part of the assembly process. The screws and slots are located in supports for the lens and LED arrays. The second part of the assembly process, adjusting the distance from the lens to the sensitive surface is accomplished with a pair of mounting brackets which are attached to the lens-LED assembly also by a set of screws and slots. These brackets contain pins and holes which mate with holes and pins on the receiving apparatus to accurately position the assembly in the apparatus. The brackets are adjusted so that the position of the assembly is accurately set with respect to the pins and slots on the brackets and thus the assembly can be placed in any machine which has the receiving slots and pins accurately positioned with respect to the photosensitive surface.
The Koek patent also shows a structure for compensating for thermal expansion differences between the LED array and its support and the lens array and its support. Because of the heat generated by the LED array such variation in thermal expansion must be compensated for in this type of apparatus.
This general arrangement has been adopted commercially and has worked quite satisfactorily. However, within this system, it is desirable to improve the accuracy and reduce the expense associated with the first step in the process, i.e., fixing the location of the lens with respect to the row of LED's.